In a modern battery production facility, the ability to form batteries is an important aspect of that facility's ability to meet fluctuating seasonal demands for fully formed and charged batteries. Since these demands peak in the winter months, it has become commonplace for manufacturers to make an inventory "duff" (dry-unformed) batteries which are filled with electrolyte and formed immediately prior to shipment during periods of peak demand. Accordingly, the "peak load" capacity of a given battery manufacturing facility depends to some extent upon the ability of that facility to form batteries.
The advent on a significant commercial scale of "maintenance free batteries" has further added to the problem of satisfying seasonal demands, since market fluctuations which may depend to a certain extent on local weather conditions make it difficult, if not impossible, to accurately predict the percentage of a given battery plant's production which must be formed as either conventional "high-antimony" product, or, alternatively, as a "maintenance free" product.
Heretofore, most battery production facilities included rectification equipment designed to supply a constant voltage to continuously charge high-antimony batteries, which voltage was selected on the basis of the formation characteristics of those batteries. For maintenance free batteries, on the other hand, which do not tend to gas as much as high-antimony batteries, which have a higher end-of-charge voltage and which may be relatively more prone to thermal runaway, relatively higher charging voltages have been preferred to effect the electro-chemical changes which occur during formation. While these constant voltage or modified constant voltage techniques have experienced considerable success, the sharp drop in currents which accompany later stages of this process significantly retard the overall formation time, particularly with maintenance free batteries which have higher end-of charge voltages.
In many battery facilities, in order to aid in formation and counteract somewhat the effect of gassing and chemical heat produced by the addition of electrolyte to dry, unformed batteries, "two shot" formation methods have been employed wherein relatively lower specific gravity acids are first introduced into the batteries and then are replaced with relatively higher specific gravity acids near the completion of the forming process to provide a "finishing charge" to those batteries. In addition to obviating certain problems with "plate pickling" which are associated with the introduction of relatively higher gravity acids to dry unformed battery, the "two shot" process of forming batteries has usually been considered to exhibit better plate clearance characteristics and more complete conversion of battery oxides into sponge lead etc. than a "one shot" process. Accordingly, most battery manufacturers have preferred a "two shot" formation process for reasons which include (1) formation time required; (2) fewer problems with overheating and/or thermal "runaway"; and (3) the clearing characteristics obtained therewith for fully charged or nearly fully charged battery plates.
Although it has long been known to utilize a variable amperage charging method for charging and/or re-charging lead acid storage batteries, variable amperage charging methods have not generally been applied by the battery industry to form storage batteries due, at least in part, to the electro-chemical complexities of such a process, particularly in view of the disparate battery capacities and types routinely formed in a normal commercial battery production facility.
Another classical formation problem in the battery industry is controlling temperature and time of battery formation. When electrolyte is first added to an unfilled, unformed battery and interacts with the paste on the plates of the element assembly within the battery, a great deal of heat is generated; this heat being referred to as the heat of neutralization. Heat continues to be generated by the battery during the formation and charging process while high current flow is presented through the batteries. It is uneconomical to purchase and maintain sufficient equipment to form batteries at a current low enough to prevent the heating of the batteries.
Various means have been devised to cool batteries during the neutralization, formation, and charging process in order to avoid internal overheating of the batteries which, if not properly controlled, results in destruction of the battery. The problem of dissipating heat which is generated during the formation of a battery has been aggravated by the widespread use of plastic battery cases throughout the automotive battery industry. Unlike rubber, composition, or glass cases previously used by the industry, plastic cases tend to have a low heat transfer coefficient which tends to insulate the interior of the battery making it particularly susceptible to overheating problems.
Several approaches, such as circulating water baths in which batteries stand in low rows of tanks permanently erected on the floor of the forming room have been used in attempts to dissipate the heat produced when using high current during the battery neutralization, formation, and charging process. While this has been successful, it is a highly restrictive technique and does not allow individual rectifying circuit control for batteries at various stages of neutralization, formation, and charging. Another method which has been used is the water spray in which the batteries are sprayed with water or cooling fluid. However this approach is not as good as the circulating bath method since the water spray does not have the heat conducting capacity of the former method. Chilled electrolyte has been used as a method of reducing the heat of neutralization. However, this is an expensive method and while it reduces the high initial peak, the possibility of high heat developing during formation exists as well as the possibility of having a delayed thermal runaway.
Due to the relatively higher volumes of batteries produced, and the plastic case designs, the various grid alloys and oxide mixtures now commonly used in the production of automotive batteries, the prior art techniques above have not proved satisfactory and relatively long formation times have therefore been necessitated to insure that overheating does not occur during formation.